Properties of Fluids
1. Which one is in a state of failure?
a) Solid
b) Liquid
c) Gas
d) Fluid
Answer & Explanations
Answer: d
Explanation: A fluid is a Tresca material with zero cohesion. In simple words, fluid is in a state of failure.
2. A small shear force is applied on an element and then removed. If the element regains it’s original position, what kind of an element can it be?
a) Solid
b) Liquid
c) Fluid
d) Gaseous
Answer & Explanations
Answer: a
Explanation: Fluids (liquids and gases) cannot resist even a small shear force and gets permanently deformed. Hence, the element must be a solid element.
3. In which type of matter, one won’t find a free surface?
a) Solid
b) Liquid
c) Gas
d) Fluid
Answer & Explanations
Answer: c
Explanation: Solid molecules have a definite shape due to large inter-molecular forces. In liquids, molecules are free to move inside the whole mass but rarely escape from itself. Thus, liquids can form free surfaces under the effect of gravity. But, in case of gases, molecules tend to escape due to low forces of attraction. Thus, gases won’t form any free surface.
4. If a person studies about a fluid which is at rest, what will you call his domain of study?
a) Fluid Mechanics
b) Fluid Statics
c) Fluid Kinematics
d) Fluid Dynamics
Answer & Explanations
Answer: b
Explanation: Fluid Mechanics deals with the study of fluid at rest or in motion with or without the consideration of forces, Fluid Statics is the study of fluid at rest, Fluid Kinematics is the study of fluid in motion without consideration of forces and Fluid Dynamics is the study of fluid in motion considering the application forces.
5. The value of the compressibility of an ideal fluid is
a) zero
b) unity
c) infinity
d) more than that of a real fluid
Answer & Explanations
Answer: a
Explanation: Ideal fluids are incompressible which means they will have zero compressibility.
6. The value of the Bulk Modulus of an ideal fluid is
a) zero
b) unity
c) infinity
d) less than that of a real fluid
Answer & Explanations
Answer: c
Explanation: Bulk modulus k is the reciprocal of compressibility fi.
k = 1⁄fi
Ideal fluids are incompressible which means fi = 0. Thus, k will be infinity.
7. The value of the viscosity of an ideal fluid is
a) zero
b) unity
c) infinity
d) more than that of a real fluid
Answer & Explanations
Answer: a
Explanation: Ideal fluids are non-viscous which means they will have zero viscosity.
8. The value of the surface tension of an ideal fluid is
a) zero
b) unity
c) infinity
d) more than that of a real fluid
Answer & Explanations
Answer: a
Explanation: Ideal fluids haze zero surface tension but real fluids have some finite value of surface tension.
10. An compressible fluid’s specific gravity was measured on earth, on a planet having acceleration due to gravity 5.5 times that of earth, and in space at STP. Where will it be having highest value?
a) on the earth
b) on the planet
c) in the space
d) it will be constant everywhere
Answer & Explanations
Answer: d
Explanation: Specific gravity is characteristic property of fluid and is independent of external conditions.
11. Should Specific Wieght of incompressible fluid only be taken at STP?
a) Yes, as specific weight may show large variation with temperature and pressure
b) No, it can be taken for any temperature and pressure
c) It should be taken at standard temperature but pressure may be any value
d) It should be taken at standard pressure but temperature may be any value
Answer & Explanations
Answer: b
Explanation: Specific weight is inversely proportional to volume. For incompressible fluid , variation of volume with temperature and pressure is negligible for practical consideration. Therefore, specific weight remains constant.
12. An instrument with air as fluid was involved in some experiment( specific volume was the characteristic property utilized) which was conducted during day in desert. Due to some reason experiment couldn’t be conducted during day and had to be conducted during night. However there were considerable errors in obtained values. What might be the reason of these errors?
a) It was human error
b) It was instrumental error
c) Error was due to the fact that experiment was conducted at night
d) None of the mentioned
Answer & Explanations
Answer: c
Explanation: In Desert areas, temperature at night is considerably lower than at day. Due to this air contracts at night. Hence, it’s specific volume changes. As specific volume was characteristic property utilized, results obtained showed error due to change in specific volume
13. Specific gravity is what kind of property?
a) Intensive
b) Extensive
c) None of the mentioned
d) It depends on external conditions
Answer & Explanations
Answer: a
Explanation: It is independent of quantity of matter present.
14. If there is bucket full of oil and bucket full of water and you are asked to lift them, which one of the two will require more effort given that volume of buckets remains same?
a) Oil bucket
b) Water bucket
c) Equal effort will be required to lift both of them
d) None of the mentioned
Answer & Explanations
Answer: b
Explanation: Density of water is more that oil. Hence, its weight for same volume of oil will also be higher. Therefore, more effort will be required.
15. For an incompressible fluid does density vary with temperature and pressure?
a) It varies for all temperature and pressure range
b) It remains constant
c) It varies only for lower values of temperature and pressure
d) It varies only for higher values of temperature and pressure
Answer & Explanations
Answer: b
Explanation: For an incompressible fluid, the change in density is negligible. Thus it does not change with temperature and pressure.
16. Water flows between two plates of which the upper one is stationary and the lower one is moving with a velocity V. What will be the velocity of the fluid in contact with the upper plate?
a) V
b) N ⁄ 2
c) 2V
d) 0
Answer & Explanations
Answer: d
Explanation: According to the No-Slip condition, the relative velocity between the plate and the fluid in contact with it must be zero. Thus, the velocity of the fluid in contact with the upper plate is 0 and that with the lower plate is V.
17. The viscous force the relative motion between the adjacent layers of a fluid in motion.
Which one of the flowing fits best in the sentence?
a) opposes
b) never affects
c) facilitates
d) may effect under certain conditions
Answer & Explanations
Answer: a
Explanation: Viscosity is the internal friction of a fluid in motion. It is the property by the virtue of which the relative motion between two adjacent fluid layers is opposed.
18. The viscosity of a fluid in motion is 1 Poise. What will be it’s viscosity (in Poise) when the fluid is at rest?
a) 0
b) 0.5
c) 1
d) 2
Answer & Explanations
Answer: c
Explanation: Viscosity is the property of a fluid and is constant for a given fluid under given conditions, irrespective of the fact whether the fluid is at rest or in motion.
19. Which of the following correctly states how the viscosities of a liquid and a gas will change with temperature?
a) Viscosity increases with the increase in temperature of a liquid and decreases with the increase in temperature of a gas
b) Viscosity increases with the increase in temperature of a liquid and increases with the increase in temperature of a gas
c) Viscosity decreases with the increase in temperature of a liquid and decreases with the increase in temperature of a gas
d) Viscosity decreases with the increase in temperature of a liquid and increases with the increase in temperature of a gas
Answer & Explanations
Answer: a
Explanation: Viscosity of a liquid is due to the cohesion between it’s molecules. With the increase in temperature of a liquid, cohesion increases, leading to the rise in viscosity. Viscosity of a gas is due to the momentum transfer between it’s molecules. With the increase in the temperature of a liquid, molecular motion increases, leading to the fall in viscosity.
20. In which types of fluids it is observed that momentum transfer dominates cohesive forces with increase in temperature and hence viscosity increases
a) Gases
b) Liquids
c) Solids
d) None of the mentioned
Answer & Explanations
Answer:a
Explanation: It is the characteristic property of gases which show increase in viscosity with increase in temperature.
21. What is the characteristic variation shown by the thixotropic fluids in their shear stress vs. rate of shear strain graph?
a) shear stress increases with increase in rate of shear strain
b) shear stress decreases with increase in rate of shear strain
c) shear stress shows variation only after a definite shear stress is reached
d) shear stress has decreasing constant and then variation relationship with rate of shear strain
Answer & Explanations
Answer: c
Explanation: Thixotropic fluid show a Non-Newtonian variation for shear stress vs. rate of shear strain graph after a characteristic limiting value of shear stress is reached.
22. What happens to viscosity in the case of incompressible fluids as temperature is increased?
a) It remains constant
b) It increases
c) It decreases
d) None of the mentioned
Answer & Explanations
Answer: c
Explanation: In case of incompressible fluids, cohesive forces govern the viscosity. As temperature increases the cohesive forces between fluid molecules decreases due to increase in molecular agitation. Hence, as a result, viscosity decreases.
23. If a fluid, which has a constant specific gravity, is taken to a planet where acceleration due to gravity is 3 times compared to its value on earth, what will happen to its kinematic viscosity.
a) It increases
b) It decreases
c) It remains constant
d) None of the above
Answer & Explanations
Answer: c
Explanation: Kinematic viscosity depends on density and dynamic viscosity. Both, density and dynamic viscosity, are independent of acceleration due to gravity. Therefore, kinematic viscosity is independent of acceleration due to gravity.
24. In liquids in order to measure the viscosity of fluid experimentally we consider the variation of shear stress with respect to what property?
a) strain
b) shear strain
c) rate of shear strain
d) none of the mentioned
Answer & Explanations
Answer: c
Explanation: By definition, viscosity is shear stress per unit ‘rate of shear strain’.
25. For a compressible fluid the kinematic viscosity is affected by temperature and pressure variation.
a) True
b) False
Answer & Explanations
Answer: a
Explanation: Viscosity shows variation for change in temperature and pressure for compressible fluids. Hence, kinematic viscosity is affected by temperature and pressure variation.
26. The kinematic viscosity of oil of specific gravity .8 is .0005 .This oil is used for lubrication of shaft of diameter .4 m and rotates at 190 rpm. Calculate the power lost in the bearing for a sleeve length of 90mm. The thickness of the oil film is 1.5mm.
a) 477.65 Watts
b) 955.31 Watts
c) 238.83 Watts
d) None of the mentioned
Answer & Explanations
Answer: a
Explanation: Power lost= torque * angular velocity
= force* radius* angular velocity
= shear stress * area* radius* angular velocity
Shear Stress = viscosity* velocity gradient
Power lost= 0.0005*0.8*1000* 2*3.142*190/60*0.2*3.142*0.23 * 190/60
= 477.65 Watts.
27. Find the kinematic viscosity of oil having density 1962 g/m3. the force experienced for area of 20 m2 is 4.904 kN and velocity of gradient at that point is 0.2/s.
a) 0.625
b) 1.25
c) 2.5
d) None of the mentioned
Answer & Explanations
Answer: a
Explanation: kinematic viscosity = dynamic viscosity / density
= (shear stress*density)/velocity gradient
= (4904* 1962)/(20*0.2)
= .625.
28. Which of the following is correct regarding the formation and collapse of vapor bubbles in a liquid?
a) Vapor bubbles are formed when the fluid pressure goes above the vapor pressure and collapses when the fluid pressure goes above the bubble pressure
b) Vapor bubbles are formed when the fluid pressure goes above the vapor pressure and collapses when the fluid pressure goes below the bubble pressure
c) Vapor bubbles are formed when the fluid pressure drops below the vapor pressure and collapses when the fluid pressure goes below the bubble pressure
d) Vapor bubbles are formed when the fluid pressure drops below the vapor pressure and collapses when the fluid pressure goes above the bubble pressure
Answer & Explanations
Answer: d
Explanation: Whenever the absolute pressure of a fluid drops below it’s vapor pressure, bubble formation starts. Again, when the fluid pressure goes above the bubble pressure, it’ll collapse. This is how cavitation formation takes place.
29. Which of the following statement is true about vapor pressure of a liquid?
a) Vapor pressure is closely related to molecular activity and temperature of the liquid
b) Vapor pressure is closely related to molecular activity but independent of the temperature of the liquid
c) Vapor pressure is not affected by molecular activity and temperature of the liquid
d) Vapor pressure is not affected by molecular activity and is independent of the temperature of the liquid
Answer & Explanations
Answer: a
Explanation: The vapor pressure of a liquid at a given temperature is given by the pressure ex-erted by the saturated vapor on the liquid surface. When the vapor is saturated, an equilibrium exists between the liquid and the vapor phases. The number of molecules leaving the liquid surface is equal to the number of molecules entering the liquid surface. Hence, it is obvious that vapor pressure will be related to molecular activity and consequently to temperature. With the increase in temperature molecular activity increases as a result of which vapor pressure increases.
30. Which of the following equation correctly depicts the relation between the vapor pressure of a liquid and it’s temperature?
a) Vapor pressure increases linearly with the increase in temperature of the liquid
b) Vapor pressure increases slightly with the increase in temperature of the liquid at low temperatures and the rate of increase goes high at higher temperatures
c) Vapor pressure increases rapidly with the increase in temperature of the liquid at low temperatures and the rate of increase goes low at higher temperatures
d) Vapor pressure remains unchanged with the increase in temperature of the liquid
Answer & Explanations
Answer: b
Explanation: Vapor pressure is closely related to molecular activity which is in turn dependant on the temperature of the liquid. With the increase in temperature molecular activity of a vapor increases slowly at first and then rapidly. Similar is the nature of variaion of vapor pressure.
31. Which of the following is the condition for the boiling of a liquid?
a) Absolute pressure of a liquid must be greater than or equal to it’s vapor pressure
b) Absolute pressure of a liquid must be less than or equal to it’s vapor pressure
c) Absolute pressure of a liquid must be equal to it’s vapor pressure
d) Absolute pressure of a liquid must be greater than it’s vapor pressure
Answer & Explanations
Answer: b
Explanation: As the absolute pressure of a liquid goes below it’s vapor pressure, the formation of vapor bubbles start. Thus, for boiling to start, the absolute pressure of a liquid must be less than or equal to it’s vapor pressure.
32. Which of the following machines have the possibility of cavitation?
a) Reaction turbines and centrifugal pumps
b) Reaction turbines and reciprocating pumps
c) Impulse turbines and centrifugal pumps
d) Impulse turbines and reciprocating pumps
Answer & Explanations
Answer: a
Explanation: Cavitation occurs whenever absolute pressure of a liquid drops below it’s vapor pressure. Dropping of pressure is observed mainly in reaction turbines and centrifugal pumps.
33. The three liquids 1, 2, and 3 with vapor pressures V1, V2 and V3 respectively, are kept under same pressure. If V1 > V2 > V3, which liquid will start boiling early?
a) liquid 1
b) liquid 2
c) liquid 3
d) they will start boiling at the same time
Answer & Explanations
Answer: a
Explanation: A liquid starts to boil whenever it’s absolute pressure drops below it’s vapor pressure. Thus, the absolute pressure of liquid 1 will drop early, as a result it’ll start boiling early.
34. Equal amount of a particular liquid is poured into three similar containers, namely 1, 2 and 3, at a temperature of T1, T2 and T3 respectively. If T1 < T2 < T3, the liquid in which container will have the highest vapor pressure?
a) container 1
b) container 2
c) container 3
d) the vapor pressure of the liquid will remain the same irrespective of it’s temperature
Answer & Explanations
Answer: c
Explanation: Higher the temperature, higher is the molecular activity and consequently, higher is the vapor pressure of a given liquid. Since, container 3 is at the highest temperature, liquid in it will have the highest vapor pressure.
35. Which one of the following is the correct relation between compressibility β and Bulk Modulus k
a) β = k
b) β = 1/k
c) β = 2k
d) β = k/2
Answer & Explanations
Answer: b
Explanation: Compressibility β of a liquid is deβned as the ratio of volumetric strain to the compressive stress while Bulk Modulus is the ratio of compressive stress to volumetric strain. Hence, β = 1/k is the correct relation.
36. Which one of the following is true about Bulk Modulus of elasticity?
a) it is the ratio of compressive stress to volumetric strain
b) it is the ratio of compressive stress to linear strain
c) it is the ratio of tensile stress to volumetric strain
d) it is the ratio of tensile stress to linear strain
Answer & Explanations
Answer: a
Explanation: Bulk Modulus k is related to the compression of a liquid and the decrease in volume per unit volume. It is the ratio of compressive stress to the volumetric strain.
37. The value of the Bulk Modulus of elasticity for an incompressible fluid is
a) zero
b) unity
c) infinity
d) very low
Answer & Explanations
Answer: c
Explanation: k = 1/β, where k= Bulk Modulus of elasticity and β= compressibility. For an incompressible fluid, β=0, thus the value of k will tend to infinity.
38. Three fluids 1, 2 and 3 have Bulk Moduli of k1, k2 and k3 respectively. If k1 > k2 > k3, which liquid will have the highest compressibility?
a) liquid 1
b) liquid 2
c) liquid 3
d) they’ll have equal compressibilities
Answer & Explanations
Answer: c
Explanation: k = 1=β, where k= Bulk Modulus of elasticity and β= compressibility. If k1 > k2 > k3, then β1 < β2 < β3. Thus, liquid 3 will have the highest compressibility.
39. Bulk Modulus, Pressure, Force, Stress – Which one of these won’t have the same unit as the others?
a) Bulk Modulus
b) Pressure
c) Force
d) Stress
Answer & Explanations
Answer: c
Explanation: The SI unit of Bulk Modulus, Pressure and Stress is N/m2 but the unit of Force is N.
40. Which of the following contribute to the reason behind the origin of surface tension?
a) only cohesive forces
b) only adhesive forces
c) neither cohesive forces nor adhesive forces
d) both cohesive forces and adhesive forces
Answer & Explanations
Answer: d
Explanation: The molecules on the surface of a liquid experience cohesive forces due to surrounding liquid molecules acting downward and adhesive forces due to surrounding gaseous molecules acting upwards. Surface tension orginates due to this unbalanced force on the surface molecules.
41. If there is no exchange of heat between system and surrounding where system comprises of a compressible fluid but the heat is generated due to friction, the process is an adiabatic.
a) True
b) False
Answer & Explanations
Answer: b
Explanation: For process to be adiabatic, there is no heat exchange and no heat generation within fluid.
42. For a compressible fluid, if there is no change in specific volume at constant temperature, what type of process it is?
a) Isothermal process
b) Adiabatic Process
c) Polytropic process
d) None of the mentioned
Answer & Explanations
Answer:a
Explanation: As, specific volume remains constant, density remains constant. Therefore for given temperature there is no change in volume. hence, the process is isothermal.
43. If the fluid is incompressible, do thermodynamic properties play an important role in its behaviour at varying temperature and pressure?
a) Yes
b) No
c) Depends on the fluid
d) None of the mentioned
Answer & Explanations
Answer: b
Explanation: If fluid is incompressible there is not much change in observed properties with variation in temperature and pressure. Hence, no perceivable change.
44. Calculate the magnitude of capillary effect in millimeters in a glass tube of 7mm diameter, when immersed in mercury. The temperature of the liquid is 25℃ and the values of surface tension of mercury at 25℃ is 0.51 N/m. The angle of contact for mercury is 130°.
a) 140
b) 280
c) 170
d) 210
Answer & Explanations
Answer: a
Explanation: Capillarity rise or fall
h=4*cosθ*σ/ρ*g*d
=4*cos130*0.51/13600*9.81*0.007
=140 mm.
45. Determine the minimum size of glass tube that can be used to measure water level if the capillary rise in the tube is restricted to 5mm. Consider surface tension of water in contact with air as 0.073 N/m
a) 5.95mm
b) 11.9mm
c) 2.97mm
d) 4.46mm
Answer & Explanations
Answer: a
Explanation: d=4*cosθ*σ/ρ*g*h
=4*1*0.073/1000*9.81*0.005
=5.95mm.
46. An oil of vicosity 7 poise is used for lubrication between shaft and sleeve. The diameter of shaft is 0.6 m and it rotates is 360 rpm. Calculate the power lost in oil for a sleeve length of 160mm. The thickness of oil film is 1.0mm
a) 25.31 kW
b) 50.62 kW
c) 37.97 kW
d) 12.65 kW
Answer & Explanations
Answer: a
Explanation: Power lost= torque * angular velocity
= force* radius* angular velocity
= shear stress * area* radius* angular velocity
Shear Stress = viscosity* velocity gradient
Power lost= 7916.8*3.142*0.3*0.3*0.3*2*3.142*60
= 25.31 kW.
47. Find the capillarity rise or fall if a capillary tube of diameter .03m is immersed in hypothetical fluid with specific gravity 6.5, surface tension 0.25 N/m and angle of contact 147°.
a) 0.44mm fall
b) 0.88mm fall
c) 0.44mm rise
d) 0.88mm rise
Answer & Explanations
Answer: a
Explanation: h=4*cosθ*σ/ρ*g*d
=4*cos147*0.25/6.5*1000*9.81*0.03
=-0.44 mm i.e 0.44 mm fall.
48. Will capillary rise occur and if it occurs what will be capillary rise if glass capillarity tube is immersed in water and experiment is carried out by astronauts in space.
a) Capillarity rise will not occur
b) Capillarity rise will occur infinitely and will come out in form of fountain
c) Capillarity rise will occur finitely and will be the whole length of tube
d) None of the mentioned
Answer & Explanations
Answer: c
Explanation: Capillary rise is given by
h=4*cosθ*σ/ρ*g*d
hence rise is inversely proportional to g
In space g is 0 m/s2
Hence, capillarity rise will occur finitely and will be the whole length of tube.
49. The surface tension of fluid in contact with air at 25℃ is 0.51N/m. The pressure inside a droplet is to be 0.05 N/cm2 greater than outside pressure. Determine the diameter of the droplet of water.
a) 4.08mm
b) 8.16mm
c) 2.04mm
d) None of the mentioned
Answer & Explanations
Answer: a
Explanation: P=4*σ/d
d= 4*.51/500
=4.08 mm.
50. If a fluid of certain surface tension and diameter is used to create a soap bubble and a liquid jet. Which of the two, bubble or liquid jet, will have greater pressure difference on the inside and outside.
a) Liquid jet
b) Soap bubble
c) Both will have same pressure differrence
d) None of the mentioned
Answer & Explanations
Answer: b
Explanation: For soap bubble,
P=8*σ/d
For liquid jet,
P=2*σ/d
Hence, soap bubble will be having more pressure difference.
51. Capillarity fall is reduced if we take the appartus (capillary tube immersed in fluid having acute angle of contact) considerable distance inside the earth( i.e below the earth crust).
a) True
b) False
Answer & Explanations
Answer: a
Explanation: Capillary rise is given by
h=4*cosθ*σ/ρ*g*d
Inside the earth, g (acceleration due to gravity) decreases. Hence, capillary rise will increase compared to that on the earth’s surface.
52. For liquid fluids will capillarity rise (or fall) increase or decrease with rise in temperature.
a) Increase
b) Decrease
c) Remain constant
d) First decrease then increase
Answer & Explanations
Answer: b
Explanation: Capillary rise is given by
h=4*cosθ*σ/ρ*g*d
As temperature increases, σ(surface tension) decreases. Therefore, correspondingly rise(or fall) will decrease as their is direct proportional relation between the two.
53. Cavitation is more pronounced in rough pipes than smooth surfaced pipes.
a) True
b) False
Answer & Explanations
Answer: a
Explanation: Rough surfaced pipes have more friction with the fluid and hence possibility of cavitation is more pronounced.
54. Two horizontal plates placed 250mm have an oil of viscosity 20 poises. Calculate the shear stress in oil if upper plate is moved with velocity of 1250mm/s.
a) 20 N/m2
b) 2 N/m2
c) 10 N/m2
d) None of the mentioned
Answer & Explanations
Answer:c
Explanation: Shear Stress = Viscosity * Velocity Gradient
= 20/10* 1.25/0.25
= 10 N/m2.
55. A water drop of diameter 1 cm breaks into 1000 similar droplets of same diameter. What will be the gain or loss in the surface energy? (Take surface tension as 0.075 N/m)
a) gain of 0.424 mJ
b) gain of 0.212 mJ
c) loss of 0.212 mJ
d) loss of 0.424 mJ
Answer & Explanations
Answer: b
Explanation: According to the Principle of Conservation of mass, M = 1000 * m, where M = mass of the big drop, m = mass of each droplet. Assuming density to be constant, D3 = 1000 * d3, i.e. D = 10d, where D = diameter of big drop, d = diameter of a droplet.
Change in surface energy = Surface tension * Change in surface area = 0:075*(1000 * πd2 – πD2) = 0:075 * (10 * πD2 – πD2) = 0:075 * 9π * (10-2)2 = 0:212 mJ Since, the change is positive, there will be a gain in the surface energy.
56. If for same temperature and pressure change, the value of bulk modulus is compared for isothermal process and adiabatic process, which one would be higher?
a) Isothermal process
b) Adiabatic process
c) Value is constant for both the processes
d) None of the mentioned
Answer & Explanations
Answer: b
Explanation: For isothermal process
K=p
For adiabatic process
K=kp
where K=Bulk modulus
k=Polytropic constant
p=Pressure.
57. The value of gas constant is same for all the gases
a) True
b) False
Answer & Explanations
Answer: b
Explanation: The value of gas constant depends on molecular weight. As the molecular weight is different, gas constant will be different.
58. Calculate the pressure exerted by 9 kg of air at a temperature of 20℃ if the volume is 0.8m3. Assuming ideal gas laws are applicable.
a) 946 kN/m2
b) 1892 kN/m2
c) 1419 kN/m2
d) None of the mentioned
Answer & Explanations
Answer: a
Explanation: Ideal gas Law: PV=nRT
n=M/m
P=(9*8314*293)/28.97=946 kN/m2.
59. A gas weighs 16 N/m3 at 30℃ and at an absolute pressure of 0.35 N/mm2. Determine the gas constant.
a) 708.23
b) 354.11
c) 531.17
d) 1062.34
Answer & Explanations
Answer:a
Explanation: R=P/(ρ*T)=3500000*9.81/16*303=708.23.
60. A cylinder of 0.8 m3 in volume contains superheated steam at 70℃ and .4 N/m2 absolute pressure. The superheated steam is compressed to .3 . Find pressure and temperature.
a) 0.74 N/m2, 422.3℃
b) 1.48 N/m2, 422.3℃
c) 0.74 N/m2, 844.6℃
d) 1.48 N/m2, 844.6℃
Answer & Explanations
Answer: a
Explanation: For polytropic process,
P2=(v1/v2)n *P1
=(0.8/0.3)1.3 * 0.4 ……..(for superheated stream n=1.3)
=.74 N/m2
T1=P1v1/nR=422.3℃.
61. Determine the compressibility of an incompressible fluid, if the pressure of the fluid is changed from 70 N/m2 to 130 N/m2. The volume of the liquid changes by 0.15 percent.
a) 0.0025 m2/N
b) 0.0050 m2/N
c) 0.0070 m2/N
d) 0.0012 m2/N
Answer & Explanations
Answer:a
Explanation: Compressibility=1/Bulk Modulus
=1/K
K=(dp*V/dv)
=60/0.15
=400
Compressibility=.0025.
62. What is the variation of cp, cv and k in case of gases when the temperature increases?
a) cp and cv decreases with temperature, and k increases
b) cp and cv increase with temperature, and k decreases
c) cp and cv increase with temperature, and k increases
d) cp and cv decreases with temperature, and k decreases
Answer & Explanations
Answer:b
Explanation: cp is molar heat capacity at constant pressure. As temperature is increased, enthalpy increases, heat capacity increases.
Same is for cv, cp is molar heat capacity at constant volume.
However cp-cv=R and cp/cv = R
Hence, as cp, cv increases R decreases.
